(1) Field of the Invention
This invention relates to a process for preparation of compositions of polyol fatty acid polyesters from plant and animal oils, reacted with isocyanates in high yield. Compositions as prepared are particularly used to produce biobased polyurethanes.
(2) Description of Related Art
Most of todays commercially available polyols are produced from petroleum. However, the depletion of petroleum combined with its increasing price in our modern societies has encouraged researchers and governments to explore new ways to produce todays polymeric materials from renewable and cheap natural resources.
Polyurethane resins are widely used in various applications ranging from medical devices to automotive body panels. The success of polyurethane is due to its ability to be produced in various forms from flexible to rigid structures. Applications include areas such as insulation, packaging, adhesives, sealants and coatings. Moreover, polyurethanes are now finding a growing market in the sector of composites for automotive applications such as seat pans, sun shades, door panels, package trays and truck box panels.
Polyurethanes are made by reaction between isocyanate groups (NCO) with hydroxyl groups (OH) when multi-functional compounds are used. A crosslinking agent or a chain extender may be used. The extent of crosslinking is crucial since it will determine the final properties such as elongation, stiffness, strength and resistance to solvents.
Most of the polyols currently used (>90%) in production of polyurethanes are either polyether and/or polyester polyols derived from petroleum, a non-renewable resource which is depleting. The price of petroleum is unpredictable, and thus so are the prices of these polyols. Moreover, the production of these polyols poses an environmental problem.
Preparation of polyols useful for polyurethane production from cheap and renewable natural oils is highly desirable in order to alleviate the present environmental threat. Natural oils consist of triglycerides of saturated and unsaturated fatty acids. One natural oil, i.e. castor oil, is a triglyceride of recinoleic acid (a fatty acid that contains hydroxyl groups) and is used to produce polyurethanes. Despite good thermal and hydrolytic stability when compared to their counterparts produced from petroleum-based polyols, these castor oil-based polyurethanes have not found a wide application. The major drawback is the limited hydroxyl content (ca. 100–170 mgKOH/g) of the oil, thus restricting its use to production of flexible and semi-rigid polyurethanes. Morever, castor oil is produced in tropical regions, which increases its cost when compared to oils such as soybean and corn for example. Therefore, other ways to make inexpensive polyols with controllable hydroxyl number from natural oils are needed.
In the case of other natural oils, they must be chemically reacted and converted to multiple hydroxyl structures useful in making of polyurethane resins. From a chemical point of view, natural oils offer two reactive sites, the double bonds of unsaturated fatty acids, and the carboxyl ester group linking the fatty acid to the glycerol.
Polyols useful for preparation of polyurethanes have been synthesized from natural oils by chemical reaction at the unsaturated sites (see U.S. Pat. No. 4,508,853 to Kluth, et al., and U.S. Pat. No. 6,107,403 to Petrovic et al.). There are two ways to make natural oil-based polyols for polyurethane preparation: (i) Epoxidation of double bonds followed by hydroxylation and (ii) the hydroformylation of double bond and subsequent hydrogenation of the carboxyl group to yield hydroxyl moieties.
In the epoxidation/hydroxylation process, the double bond is converted into an epoxy group that is further opened in acidic solution. Usually, the conversion to the epoxy is performed by a peroxyacid or peroxide. Reaction is carried out in the presence of a common solvent for both the peroxyacid and the oil or in a bi-phasic medium and depending on the reagents used a lot of side products can be formed.
In the hydroformylation/hydrogenation process, the oil is hydroformylated in a reactor filled with a mixture of hydrogen (H2) and carbon monoxide (CO) in the presence of a suitable organometallic catalyst (cobalt and rhodium catalysts work best) to form the aldehyde, which is subsequently hydrogenated in presence of a cobalt or nickel catalyst to form the required polyol. The reaction is carried out in a reactor.
These ways of making polyol from natural oils are limited to oils containing double bonds whose conversions to hydroxyl groups are not always well controlled. Indeed, undesirable aldehyde and epoxy groups are sometimes found in the polyol. Moreover, polyols with a high hydroxyl content (>250 mg KOH/g) are difficult to obtain. Besides, the use of a large number of reactants like peroxyacid, peroxide, hydrogen and carbon monoxide gases not only make the synthesis and processing more complicated with several byproducts whose removal to make pure polyol makes the process more energy intensive but also increase the overall cost of the resulting polyol. In addition, risks are associated with the use of reactants such as hydrogen and carbon monoxide gases and also peroxyacids (like m-chloroperbenzoic acid) and peroxide.
Some progress has been realized in the making of polyols for polyurethane preparation from natural oils by reaction at their carboxyl ester groups. In a patent (WO 01/04225 A1), Shah et al mixed vegetable oils with polyhydroxy alcohols such as glycerol in the presence of carboxylic acids and a catalyst under nitrogen atmosphere. In another recent patent, Kurth et al (U.S. Publication No. 2002/0058744 A1) described the preparation of vegetable oil-based polyols in a two-stage process. In the first stage they prepared a reaction product mixture of multifunctional alcohol and saccharide that reacts in the second stage with a vegetable oil in presence of a transesterification catalyst. The disclosure of this application is incorporated by reference herein.
Other pertinent applications and publications are: U.S. Pat. No. 4,518,722 to Volpenheim, U.S. Pat. No. 5,006,648 to Pleun Van der Plant, et al., U.S. Pat. No. 5,596,085 to Silver et al., and U.S. Pat. No. 4,812,533 to Simone et al. These are also incorporated by reference.
Objects
In accordance with the current invention, it is an object to overcome the deficiencies found in the described processes for making natural oil-based polyols in a cost effective one-stage process and to use them for making biobased polyurethanes. A further object of this invention is the control over the hydroxyl content of polyols and thus the possible tuning of the mechanical properties of the subsequent polyurethanes through the control of crosslinking within the polymer network. A further object is to provide a process which is ‘green’ and eco-friendly. It is finally an object to provide biobased polyurethanes which can be used in various applications as matrix for biocomposites, resins, foams and coatings.